In a conventional residential sewer collection system, discharge from various receptacles present in the interior plumbing arrangement drains into a vertical collection line and then into a sewage collection line. Households are usually connected to the sewer line by clay, cast-iron, or polyvinyl chloride (PVC) pipes 3 to 4 inches in diameter. The sewage collection line conducts sewage collected from various receptacles present in the interior plumbing into a sewer main or septic tank. Unlike water-supply systems, wastewater flows through sewer pipes by gravity rather than by pressure. Due to the lack of pressure, blockages can occur in the sewer collection line, which can have the very unpleasant result of sewer water backing up in sinks, toilets, and bathtubs. This is a particular problem for multi-story buildings, since the sewer lines on the lower floor can become clogged while higher stories continue to empty water into the sewer line, which can cause the lower floors to be flooded with sewer water. 
Building codes require sewer systems to have clean outs which provide access to clear blockages in the sewage collection line as may occur over time with the line becoming partially blocked by tree roots or other foreign objects. The clean out allows the blockage to be reached using tools such as plumbing snakes. The clean out is usually a vertical conduit extending from the sewage line to a point at or near ground level. The upper end of the clean out has internal threads so that a cap or fitting with mated threads can be screwed therein.
It is well known in the art to replace the clean out cap with an escape valve so that sewage back up will overflow through the clean out, instead of overflowing into toilets, sinks etc. Some prior art patents are directed to blow-out type caps ejectable by pressure present in the pipes, such as U.S. Pat. Nos. 4,261,386, 3,895,466, and 4,850,059. Valve type sewer backflow preventors include U.S. Pat. No. 5,645,099, 4,917,147, 4,215,724.
Baker, Jr., U.S. Pat. No. 5,209,257, discloses a vent for relieving pressure in a sewer system which comprises a threaded plug having a buoyant float closure seated therein. The elongated configuration causes the float to reseat itself.
Westerhoff, U.S. Pat. No. 3,805,826, discloses a relief valve which is substituted for the normal plug which comprises two concentric cylindrical portions slidable with respect to one another. The upper portion is sealed at the top, and includes side vents for discharge. A screw keeps the upper portion from being  ejected by pressure.
Several prior art patents disclose an arrangement wherein an audible buzzer is activated in the event of an overflow. For example, Young et al., U.S. Pat. No. 4,392,128, Allen, U.S. Pat. No. 4,091,365, and Statz, U.S. Pat. No. 4,398,186 each discloses a device where an electric circuit is closed by the mechanical action caused by the rising water to set off a warning alarm.
The prior art systems are effective to provide a means by which backflow into interior plumbing fixtures is prevented. While it is certainly preferable that the sewage backflow overflow in an outdoor environment rather than inside, the presence of the effluent on the ground can create a health hazard. Children and pets in particular can easily come into contact with the unsanitary ground area.
Thus, what is needed is a means to chemically treat sewage water overflowing from a clean out in order to reduce or eliminate harmful bacteria present in the sewage overflow, as well as to neutralize foul odors. The present invention overcomes the drawbacks of the prior art devices by providing a sewer clean out cap which functions as an overflow valve, and which also includes an integral means of disinfecting sewer effluent as it flows through the device so that the immediate environment is not contaminated. 